1. Field of the Invention
The present invention relates to a cathode having improved conductivity and hardness and a method for making the cathode.
This invention is further directed to electrolytic cells, e.g., solid batteries, containing the cathode.
2. State of the Art
Electrolytic cells containing an anode, a cathode, and a solid solvent-containing electrolyte are known in the art and are usually referred to as "solid batteries". These cells offer a number of advantages over electrolytic cells containing a liquid electrolyte (i.e., "liquid batteries") including improved safety features.
The cathode employed in such a cell is typically comprised of a compatible cathodic material (i.e., insertion compounds) which is any material which functions as a positive pole in a solid electrolytic cell. Such compatible cathodic materials are well known in the art and include, by way of example, manganese dioxide, molybdenum trioxide, oxides of vanadium such as V.sub.6 O.sub.13, V.sub.2 O.sub.5, LiV.sub.3 O.sub.8, and the like, sulfides of titanium and niobium, chromium oxide, copper oxide, and the like.
In preparing a cathode, the compatible cathodic material can for example, be mixed with an electroconductive material including, by way of example, graphite powdered carbon, powdered nickel, metal particles, conductive polymers (i.e., characterized by a conjugated network of double bonds like polypyrol and polyacetylene), and the like, and a binder such as poly(tetrafluoroethylene) to form under pressure a cathodic plate.
It has also been recognized that the cathode can be prepared from a cathode paste which comprises from about 35 to about 65 weight percent of a compatible cathodic material; from about 1 to 20 weight percent of an electroconductive material; up to about 20 weight percent of polyethylene oxide having a number average molecular weight of at least 100,000; from about 10 to 50 weight percent of a suitable solvent; and from at least about 5 weight percent to about 30 weight percent of a solid matrix forming monomer or partial polymer thereof. (All weight percents are based on the total weight of the cathode).
In the production of the paste, the components are typically simultaneously mixed together. Moreover, in such an arrangement, the polyethylene oxide is typically introduced into the other solids in the system, e.g., the compatible cathodic material and the electroconductive material.
The cathode paste is spread onto a suitable support such as current collector and cured by conventional methods to provide for a solid positive cathodic plate. The cathode (excluding the support) generally has a thickness of about 20 to about 150 microns.
Current collectors are well recognized in the art some of which are commercially available. A typical current collector for the cathode is a roughened nickel (electrolytically deposited nickel) on nickel current collector (available as CF18/NiT from Fukuda Metal Foil & Powder Company, Ltd., Kyoto, Japan). The current collectors are typically attached to the surface of the cathode not facing the electrode but can also be attached to the anode. When the current collector is attached to the cathode, the cathode is interposed between the electrolyte and the current collector.